High-frequency fluorescent tube lighting circuit and ac driving circuit therefor

ABSTRACT

A sinusoidal voltage source in series with a fluorescent, mercury vapor, sodium vapor device, etc. is pulsed at a given pulse repetition rate with the pulse having a given conduction time. Two or more tubes can sequentially conduct pulses with the current input being a continuous sinusoid. A particular pulsing circuit contains a modified pulse-forming network consisting of one or more stages of a closed series connection of a choke and two capacitors. The chokes of each stage are connected in series. The modified pulse-forming network is used as a frequency converter per se, as DC to AC converter, or specifically is in parallel with a fluorescent tube load.

ali Unite States atent 1 1 3,619,716

[72] Inventors Joel S. Spira [56] References Cited fzf s h ks UNITEDSTATES PATENTS c 2,936,420 /1960 Tyler 328/27 [21] Appl. No. 843,927[72} F1 3,037,147 5/1962 Genu1t et al. 315/289 X 1 ed July 23, 1969 P3,243,711 3/1966 King et a1 323/22 1971 3 320 521 5/1967 S t 1 323 74[73] Assignee Lutron Electronics Co., Inc. egawae a Emmaus, p FOREIGNPATENTS 793,582 4/1958 Great Britain 315/100T Primary Examiner-Roy LakeAssistant Examiner-E. R. LaRoche Attorney0strolenk, Faber, Gerb & Soffen[54] HIGH-FREQUENCY FLUORESCENT TUBE Z SS AND AC DRIVING CIRCUITABSTRACT: A sinusoidal voltage source in series with 21 Claims lsnrawinFi fluorescent, mercury vapor, sodium vapor device, etc. is g pulsed ata given pulse repetition rate with the pulse having a [52] US. Cl315/244, given conduction time. Two or more tubes can sequentially315/105,315/208,315/235,315/242,315/290, conduct pulses with the currentinput being a continuous 315/D1G.2,315/D1G.5,328/27,328/223 sinusoid. Aparticular pulsing circuit contains a modified [51] Int. Cl 1105b41/233, pulse-forming network consisting of one or more stages of a1105b 41/392 closed series connection of a choke and two capacitors. TheField of Search 315/94, 98, chokes of each stage are connected inSeries. The modified pulse-forming network is used as a frequencyconverter per Se, as DC to AC converter, or specifically is in parallelwith a fluorescent tube load.

PATENTEDHUV 9 ISYI 3.619.716

SHEET 3 OF 3 HIGH-FREQUENCY FLUORESCENT TUBE LIGHTING CIRCUIT AND ACDRIVING CIRCUIT THEREFOR This invention relates to AC power supplies,and more particularly relates to AC power supplies for gas dischargetube lighting which eliminates the need for a ballast or otherinductances which are normally connected to gas discharge lamps.

A common gas discharge lamp which is operated from a 60 cycle source iscommonly provided with a so-called ballast which consists of aninductance (or resistor) connected in series with the lamp. This ballastserves several functions. One function is to limit lamp current whichwould otherwise increase uncontrollably due to the negative resistancecharacteristic of the electric discharge in the lamp. Another purpose isto obtain lamp starting and voltage regulation. Thus, a lamp may requirea relatively high starting (striking) voltage, but, after the arc isinitiated, will have a considerably lower operating voltage. The seriesballast will then absorb the difference between line voltage and lampoperating voltage. Note that full line voltage, or greater, is needed tostrike the lamp arc to initiate conduction. A third major function ofthe ballast in certain types of tubes is to provide a transformer ofautotransformer which can supply cathode filament voltage, and a voltagesurge for initiating arc discharge.

Ballasts using a series resistor are relatively inefficient and are notcommonly used. Normally, the ballast takes the form of a seriesinductance or transformer. Where these ballasts are used in the usualsixty cycle circuit, they are large, heavy, noisy and expensive.Moreover, the need for the ballast must be considered in the design ofthe lamp fixture. In order to limit the size and expense of ballasts,fluorescent circuits have been operated from high-frequency powersources having frequencies up to a few thousand cycles per second. Theuse of higher frequencies is also advantageous in the operation of afluorescent lamp since, at higher frequencies (than 60 cycles) the lamphas greater lumen efficiency, (increased lumens per watt) longer lifeand easier starting.

When using higher frequencies to drive fluorescent tubes, and having asixty cycle source available, it is necessary to provide frequencychanging apparatus such as mechanical rotating converters or electronicfrequency converters. The size and expense of such conversion equipmentoften offsets the advantages of decreased ballast size and increasedlamp efficiency. Moreover, the use of converters frequently requiresspecial wiring mains and branch circuits of limited capacity, anddecreases the reliability of the lighting system. Consequently, the useof higher frequency sources for fluorescent lighting has not gained widecommercial acceptance.

In accordance with one aspect of the present invention, a switchingmeans is connected with the 60 cycle source and the fluorescent tube,and operates to turn on and off at a given frequency within the 60 cyclewaveform. For example, the switching means may be conductive or ON for100 microseconds, and nonconductive or OFF for 900 microseconds, wherebya l,000 cycle fundamental is introduced into the 60 cycle wave shape.Obviously, the OFF" times and ON times can be varied in any desiredratio to one another and have various repetition frequencies. As will belater described, the pulsing circuit may drive a delay linepulse-forming network which is in parallel with the tube and which isper se novel for use as a DC to AC converter or frequency changer. Theswitching means, as used in the novel combination of the invention (witha gas discharge tube) may use conventional switching circuitsincorporating controlled rectifiers, transistors, and the like.

The modulation of a low-frequency (frequencies such as 50 or 60 cyclesper second, used in lighting circuits) sine wave form at various ON"times and pulse repetition frequencies introduces many desirable effectsin a fluorescent lighting circuit. A major advantage is that theconventional ballast can be eliminated. That is, the conduction time isshort so that a current-limiting impedance is not needed or can beprovided by various simple and small resistors, inductances orcapacitors, or combinations thereof. Output regulation may now beprovided by varying either pulse repetition frequency or the ON time.Cathode filament voltage may now be extracted from the modulated sinewave by transformers which are small and inexpensive and tuned to thehigh modulating frequency. Since the tube is driven at the highmodulating frequency, it is subject to all the advantages of increasedlumen efficiency, longer life and easier starting. Since the ballast canbe eliminated, noise, size, weight and cost of the system issubstantially decreased. At higher frequencies, noise is eliminated orgreatly reduced by virtue of smaller and simpler inductive andcapacitive components and also eliminated by operating at a frequencyabove the audio range. Moreover, the heat generated by the novel systemis less than in a conventional ballast system so that the lamps can beoperated more efficiently at higher current and light levels.

The novel system of the invention also lends itself to the complementaryconduction of two or more lamps, thereby reducing complexity and radiofrequency interference. Thus, the low-frequency AC source may conduct acontinuous sine wave current. This current is thus sequentially switchedbetween two or more lamps, each sequentially conducting for a given ONtime. This arrangement permits a saving in hardware and reduces radiofrequency interference since the power input will be a continuouslow-frequency sine wave instead of a chopped sine wave.

It is also possible to use a common switching means or modulator foreach of a large number of tubes. Thus, a single modulator could serve 10lamps or more so that the cost of the modulator per lamp becomes verysmall.

The novel combination of the invention also lends itself to light outputregulation and to automatic regulation of light with line voltagechange. Thus, light output can be changed by changing the conductiontime of the lamp. A potentiometer type adjustment could thereforeprovide controlled dimming of a fluorescent lamp. It is also possible tomaintain constant illumination when input voltage changes by providing asuitable control circuit which varies conduction time inversely withchanges in line voltage.

In accordance with an important feature of the invention, the lamp maybe connected in parallel with a delay line type network previouslyadjusted to be used as a pulse-forming network. Such a circuit may beused as frequency converter per se or as a DC to AC converter per se inaccordance with an important feature of the invention. This networkconsists of series-connected chokes with capacitors connected at thejunctions of the various chokes. In particular, each section of thedelay line consists of at least one inductor and at least one capacitor,connected in a closed series circuit. A single section can be used forthe present invention. A network of this type is shown in pages 10 and11, chapter 6, in the text Principles of Radar, published by McGraw HillCo., Inc., 1946 (second edition). Circuits of this type are used forforming a square pulse in the driver stage of a radar modulator. Inaccordance with the invention, a circuit of this type is so adjustedthat it will oscillate, whereby the circuit is initially charged for ashort charging time from the pulsing circuit and thereafter (during theOFF time of the pulsing circuit, or modulator) provides an oscillatingdischarge which is connected to any suitable load, such as a fluorescenttube. It will be shown that the wave shape output of this novelmodulator, while not completely sinusoidal, is satisfactory for drivinggas discharge tubes, and would also be satisfactory for any applicationwhich does not require an accurate sinusoidal wave shape. The chokesused in the delay line oscillators may contain one or more windings toprovide filament heating windings and the like.

An important feature of the various circuits that can be constructed inaccordance with the invention is that there is a significant ACcomponent in the voltage applied to the tube, if not a pure AC voltage.In particular, in a current fed mode, to be described hereinafter, thereis a pure AC voltage input to the tube whether the energizing circuit isan AC or DC circuit. This has a significant advantage since most gasdischarge lamps are most efiiciently operated when an AC voltage isconnected to the lamp. While most gas discharge lamps can be operatedfrom either DC or AC voltage, DC voltage will cause a prematureblackening or darkening at one end of certain types of gas dischargelamps, particularly fluorescent lamps. DC operation is also lessefficient than AC operation. For example, lamp efficiency for DCoperation is about 70 percent of its efiiciency at high-frequency ACoperation. DC operation will also cause decreased fluorescent tube lifeby 10 to 20 percent. Where DC voltage is applied to mercury vapor lamps,there is a loss in life time because of overheating of one electrode. Insome sodium vapor lamps, the lamps cannot be operated at all by DCvoltage. The main advantage of DC operation is that it does not cause astroboscopic effect. However, devices operated in accordance with thepresent invention are operated at sufficiently high frequency toeliminate any strobos'copic problem.

Accordingly, a primary object of this invention is to provide a novelenergizing circuit for gas discharge tubes which eliminates theconventional ballast, and operates the tubes at a relatively highfrequency.

Another object of this invention is to provide a novel drive circuit forgas discharge tubes which controllably modulates a sine wave at a givenpulse repetition frequency and a given conduction time for each pulse.

Still another object of this invention is to operate a plurality of gasdischarge tubes from an AC circuit which is switched between the varioustubes to establish a given pulse repetition frequency and conductiontime for each tube.

Another object of this invention is to provide a novel common energizingcircuit for a plurality of gas discharge tubes and for eliminating theballast of the tubes.

A further object of this invention is to provide a novel, simple andinexpensive frequency converter or DC to AC converter which is formed ofa modified pulse-forming network.

These and other objects of this invention will become apparent from thefollowing description when taken in connection with the drawings, inwhich:

FIG. 1 is a circuit diagram of the combination of modulator and gasdischarge tube of the present invention.

FIG. 2 schematically shows two gate controlled switches which could beused in the modulator circuit of FIG. 1.

FIG. 3 shows the output pulse current of the modulator of FIGS. 1 and 2when the modulator is driven from a sinusoidal voltage source.

FIG. 4 shows the output pulse current of a circuit similar to that ofFIG. 1 when the modulator is driven from a DC source.

FIG. 5 illustrates the manner in which a plurality of tubes can share acontinuous sine wave current input.

FIG. 6 illustrates the division of current pulses in. the circuit ofFIG. 5.

FIG. 7 shows a circuit diagram similar to FIG. 1 which includes linevoltage regulation.

FIG. 8 illustrates the use of a delay line network in a circuit using amodulator and gas discharge tube load with the delay line connected in avoltage fed mode.

FIG. 9 is similar to FIG. 8 and shows the delay line connected in a'current fed mode.

FIG. 10 shows the current-time characteristic of FIG. 9 when the loadimpedance is greater than the network characteristic impedance.

FIG. 11 shows the current-time characteristic of FIG. 9 when loadimpedance is about equal to the network characteristic impedance.

FIG. 12 shows the current-time characteristic of FIG. 9 when loadimpedance is about equal to the network characteristic impedance and thepulse-charging time is close to the pulse period.

FIG. 15 is similar to FIG. 14 but uses individual oscillation networkswhich are modifications of the network shown in FIG. 8.

Referring first to FIG. 1, there is shown a circuit which illustratesthe principle of the present invention wherein a voltage source isconnected to terminals 20 and 21 and in series with pulse modulator 22,a gas discharge tube 23 and a currentlimiting impedance 24. Tube 23 maybe of any desired commercially available variety. It is possible toeliminate this impedance if the conduction time of tube 23 is madesufficiently short. When conduction time is made sufficiently short,ionization does not have time to build up to a high degree. For example,with a small neon tube, a pulse time of less than about 6 microsecondscan be used. Therefore, the effective impedance of the lamp isrelatively high and the current could not build up to extremely highvalue, and thus the tube would operate satisfactorily while not burningout due to excessive heating. Where the tube 23 has hot cathodefilaments, a filament current supply can be provided by transformer 25which has filament heater windings 26 and 27. Transformer 25 could havebeen an autotransformer, and could have been arranged in series withtube 23. A suitable starting circuit (not shown) may be provided ifneeded for the particular tube selected.

The voltage source connected to terminals 20 and 21 could be a standardlow frequency AC source, where low frequency is intended to refer to theusual frequencies used in home lighting and commercial lighting circuitssuch as 50 or 60 cycles. FIG. 3 shows the sinusoidal voltage wave formof this low-frequency source as dotted line 28.

The modulator 22 is constructed as a pulse modulator, and, accordingly,applies the pulse voltage shown in FIG. 3 to the tube. The pulserepetition frequency is shown to be about 1,000 cycles per second inFIG. 3 and may vary from about 200 cycles per second to any desiredupper frequency limit. The modulator, and thus the pulse current maytypically have a conduction time of about 100 microseconds andnonconductive time of about 900 microseconds. These times can be variedas desired. It has been found that once the tube 23 has been ignited, itneed not be reignited with each successive voltage pulse from modulator22. That is, the deionizing time of the tube is sufficiently long thatthe tube is not deionized between successive voltage pulses when thepulse repetition frequency is sufficiently high.

Since the tube 23 is now driven by a relatively high-frequency source,the transformer 25 will be smaller than the equivalent transformer whichis designed for low-frequency operation. Moreover, transformer 25 willbe appropriately tuned for operation at the relatively high frequency.Similarly, the current-limiting impedance, which could be a reactivetype component, will have a smaller size as the frequency of the currentconducted thereby is increased. Moreover, since tube 23 is driven at arelatively high frequency, it will have an increased lumen efficiencyand longer life. Moreover, by making the modulator in such a manner thatpulse length can be controlled, the output of lamp 23 can be controlledor dimmed."

Modulator 22 may be made in any desired manner, for example, as shown inFIG. 2, the modulator 22 may include two back-to-back connectedgate-controlled switches 29 and 30 which are conductive so long as agate signal is applied to their gates 31 and 32, respectively. Asuitable pulse timing circuit 33 is then connected to gates 31 and 32and delivers timed firing pulses to gates 31 and 32.

It has been found possible to apply a DC source to terminals 20 and 21,with modulator 22 generating pulses from the DC source as shown in FIG.4. Thus, while the DC voltage, shown by dotted lines 34, is below thetube striking voltage, once the tube is fired, the pulse repetition timeis less than the deioniz FIG. 13 shows a circuit diagram of a particularcircuit '70 ing time of the tubeso that the tube will operate with eachsucsimilar to the circuit of FIG. 9.

FIG. 14 shows a circuit using the general concepts of the circuit ofFIG. 9 where, however, a plurality of lamps and plurality of oscillationnetworks for each lamp are used with a common pulse modulator.

herein. Any suitable means could be used to insure proper striking andconduction of all of such parallel connected tubes. Thus considerableeconomy is achieved in the savings of the ballasts for each lamp, andthe cost of the modulator per each lamp of a large number becomes verysmall. Moreover, the modulator 22 can be combined in the same wall boxwith the ON-OFF switch 35 so that the designer of the fixture for lamp23 (or a plurality of such lamps) need not consider the bulk ofaballast, or the housing for modulator 22, in his fixture design.

In accordance with a further feature of the invention, a plurality oftubes can be arranged to sequentially share current pulses from acontinuous sinusoidal current supply. FIG. 5 shows a circuit in whichthree tubes 40, 41 and 42 (which could be respective groups of tubes)are connected in series with terminals 20 and 21 (as in FIG. 1) whichare connected to a suitable low-frequency source. Each of tubes 40, 41and 42 are then connected in series with respective pulse modulators,shown as back-to-back pairs of gate-controlled switches 43-44, 45-46 and47-48, respectively. Each of the pairs of switches is provided with arespective pulse timing circuit, such as pulse timing circuits 49, 50and 51, respectively, which causes the current from terminals 50 and 51to sequentially switch or commutate from tube 40 to tube 41 to tube 42and back to tube 40, etc. Thus, a continuous and sinusoidal current isdrawn from the source connected to terminals 20 and 21, therebysubstantially decreasing radio interference.

This continuous sinusoidal current wave form is shown in FIG. 6.Referring to FIG. 6, the current pulse to tubes 40, 41 and 42 is shownrespectively as the cross-hatched pulses (labeled l in which the hatchlines rise from left to right, as the cross-hatched pulses (labeled 2)in which the hatch lines fall from left to right, and as thedouble-hatched pulses (labeled 3). Clearly, the envelope of the currentpulses of FIG. 6 defines a continuous sinusoid.

Note that HGS. 5 and 6 require that the pulse OFF time is twice as longas the pulse ON time since three tubes share the total sinusoid current.Clearly, any desired number of tubes could be used to share the totalcurrent with the ratio of ON" to OFF pulse time being suitably adjusted.

The use of a pulse modulator permits many desirable control functions inthe lighting circuit. As previously stated, it permits dimming bycontrolling the length of the conducting pulse in the circuit of FIG. 1.FIG. 7 shows the manner in which the novel concept can be used to offsetthe effect of varying line voltage. Note that the circuit of FIG. 7 usesthe modulator of FIG. 2 in the circuit of FIG. 1 and shows a choke 50 asthe current-limiting impedance. Thus in FIG. 7, the terminals 20 and 21are connected to an AC source which has a varying voltage. This wouldnormally vary the intensity of the output of tube 23. In accordance withthe invention, the pulse timing circuit is further provided with asuitable circuit for changing pulse conduction time in response tovarying line voltage. Thus, a potential transformer 51 is connectedacross terminals 20 and 21 and applies a input voltage to the pulsetiming circuit. The pulse timing circuit is suitably arranged so thatpulse conduction time, or the pulse repetition frequency, is variedinversely with the output voltage of transformer 51. A decrease in linevoltage will, therefore, increase the pulse length so that lightintensity can be held constant. Similarly, an increase in line voltagewill decrease pulse time so that light intensity will be constant. Anadjustable resistor 52 can be connected in series with the output oftransformer 51 and serve for manual adjustment of output lightintensity, or dimming."

FIGS. 8 and 9 illustrate embodiments of the invention in which the pulsemodulator is followed by an oscillator-type circuit formed of a modifiedpulse-forming network with the combination operating to provide ahigh-frequency current output to one or more fluorescent lamps.

Referring to FIG. 9, there is shown a circuit having input terminals 60and 61, a modulator 62, an oscillating network 74 and a fluorescent lump64. Either a low-frequency AC power source or a DC source can beconnected to terminals 60 and 61, as previously described in connectionwith FIG. 1. The modulator 62 may be the same as the modulator 22 ofFIGS. 1 and 2, it only being necessary that modulator 62 acts to pulsethe voltage connected to terminals 60 and 61. Lamp 64 may be of anydesired type.

Network 74 is connected in a current fed mode (a shorted delay line) andconsists of two chokes 71 and 72, and capacitor 73 connected as shown.Circuits of this type (with additional stages) are well known as delayline-pulse shaping circuits for radar modulators.

In accordance with the present invention, this type circuit which shallbe termed as oscillation network hereinafter, follows the pulsemodulator and acts to provide an oscillating output current having agenerally sinusoidal characteristic wave shape.

FIGS. 10, 11 and 12 show the current applied to tube 64 from theoscillation network 74 for various designs of the network 74. FIG. 10shows the system when the impedance of tube 64 is substantially larger(for example, 5 times) than the characteristic impedance of network 74.In FIG. 10, pulses 75 and 76 are the pulses delivered from modulator62-. These pulses have a period T and a conductive time t. These pulsescan be considered to charge network 74 which subsequently oscillateswith a period 20 as shown in FIG. 10. Thus, in period T, tube 64 willhave six current pulses applied thereto (including pulse 75) with awaveform approximating a sine wave. Note that the closer the pulse timeis to 0, the closer the wave shape is to a sinusoid. Therefore, if thepulse repetition frequency of modulator 62 is I,000 p.p.s., the tube 64will carry a driving current of about 6,000 cycles per second.

As shown in FIG. 10, the circuit has a resonant ring since the loadimpedance is much greater than the characteristic impedance of network74. The network can be made nonresonant, as shown in FIGS. 11 and 12, bymaking the load impedance about equal to the network characteristicimpedance. Thus, in FIG. 11, a sinusoid is obtained with the period T ofpulses 75 and 76 approximately equal to (20+t). A better or smootherwaveform is obtained in FIG. 12 by reducing the period T of pulses 75and 76 with respect to the oscillation period 20, and by making T=0+t,and t approximately equal to 0.

An important advantage of the circuit of FIG. 9 is that it provides anessentially pure AC input to the tube, even though a DC operatingvoltage is applied to terminals 60 and 61.

In one particular test that was performed on a circuit of the type shownin FIG. 9, a DC voltage was connected to terminals 60 and 61, which wassuch that approximately volts AC was measured across the terminals oflamp 64. The DC content of this AC voltage was measured to be less than0.2 volts. This DC component is believed to be present since the chokes71 and 72 represent a short circuit to DC current so that the 0.2 voltswas an IR drop across the coils. Obviously, this IR drop could be evenfurther reduced by merely using windings for the coils which have alower resistance.

In the case of the current fed pulse-forming network of FIG. 9, startingmay be automatic. When the tube is OFF, its impedance is extremely high(in the order of megohms), and thus the tube impedance is very muchgreater than the characteristics impedance of the network, regardless ofthe ratio of load impedance to tube impedance selected in accordancewith FIGS. 10, 11 and 12. Thus, the network, during starting, willsupply very high voltage pulses to the tube, thereby firing it. It isalso possible to wind a few turns on choke 71 or 72 and drive thefilaments with these turns to effect completely selfcontained startingand operation for a rapid start lamp.

Another technique for starting may use inductance in the circuit whichis adjusted for low Q when the tube is operating. However, when the tubeis OFF the inductance has a higher Q and comes out of saturation,therefore generating a high voltage for starting.

FIG. 8 is similar to the circuit of FIG. 9, but operates in a voltagefed mode rather than a current fed mode. Thus, in

FIG. 8 the oscillation network 63 is connected in parallel with tube 64and consists of chokes 64 and 65 and capacitors 66 and 67. The circuitoperates in a similar fashion as previously described in connection withFIGS. l0, l1 and 12.

In the foregoing, the combination of an AC or DC voltage source, amodulator and an oscillation network have been described in connectionwith a fluorescent lamp load. It should be understood, however, that anytype load could have been used, particularly where the load impedance ismuch greater (for the current fed case) than the network characteristicimpedance (as in FIG. Thus, the circuit can operate as a frequencyconverter per se when the input to terminals 60 and 61 of FIGS. 8 and9is AC or as a DC to AC converter if DC is applied to terminals 60 and61. FIG. 13 shows a circuit which was constructed to carry out thecurrent fed mode of operation described in FIG. 9. Referring to FIG. 13,the power source consisted of a 120 volt, 60-cycle source connected toterminals 80 and 81 of a variable transformer 82. The output of variabletransformer 82 is variable between 0 to 140 volts and is connected to anisolation transformer 83. The isolation transformer secondary winding isthen connected to a full wave rectifier bridge 84 which supplies a DCinput voltage to the pulse modulator portion of the circuit.

The pulse modulator was formed of the circuit shown within dotted block85 and is equivalent to modulator 22 of FIG. 1 or modulator 62 of FIGS.8 and 9. The modulator 85 has input terminals 86 and 87 which areconnected to a suitable pulse timing circuit. Any standard pulse timingcircuit could be connected to terminals 86 and 87, and, for experimentalpurposes, a commercially available pulse generator, manufactured by'Iektronics Corporation was used as a source of timing pulses.

A resistor 88 (47 ohms) is provided across terminals 86 and 87 toterminate the pulse generator and a resistor 89 (2.2K) connected to thebase of transistor 90 (2N4037) and serves as a current limiting andisolating resistor. The collector of transistor 90 is connected to thebase of transistor 91 (2N4037. The collector of transistor 91 is in turnconnected to the base of power transistor 92 (M1423) through resistor 98l0 ohms).

Suitable decoupling resistors 93 (33 ohms), 94 (330 ohms), 95 (33 ohms)and 99 1K) are provided along with decoupling capacitors 96 (50microfarads) and 97 (50 microfarads). Each of resistors 93, 94, 95 and99 were connected to biasing voltage sources as indicated which wereprovided by batteries. Clearly, a standard rectifier power supply couldbe used for this purpose.

The emitter-collector circuit of power transistor 92 is then connectedin series with the output of rectifier 84, diode 100 (lN647), andresistor 101 (IOK). Diode 100 protects transistor 92 against voltagereversal and resistor 101 dissipates energy from the oscillating networkwhen the lamp is turned off, as will be described. The lamp wasfluorescent lamp 110 which was a 40-watt lamp manufactured by Sylvaniatype F40CW Life Line." A metal foil starting aid to simulate the fixture111a, shown in dotted lines, was placed along the tube and connected toone of its electrodes as shown. The cathode filaments of lamp 110 wereheated by two 6-volt batteries 112 and l 13, it being obvious that asuitable transformer circuit could be used for this purpose.

The oscillating network was then formed of chokes 120, I21 and 122 andcapacitors 123 and 124. Note that the network is connected in thecurrent-fed mode of FIG. 9. Each of chokes I20, 121 and 122 had aninductance of 1.7 millihenrys and each of capacitors I23 and 124 were0.I7 microfarad, 400 volt capacitors.

The circuit of FIG. 13 operates as follows:

When a positive pulse is applied to terminals 86 and 87, transistor 90,which is biased to normally conduct, is turned off. This turns thetransistor 91 on, transistor 91 being biased to be normally off. Theconduction of transistor 91 causes transistor 92 to turn on, transistor91 being normally off. Thus a positive going pulse applied to terminals86 and 87 turns transistor 92 on for the duration of the input pulse.

When transistor 92 turns on, the output voltage of rectifier 84 appearsacross resistor 101 and thus across the oscillating network and tube110. The oscillating network, consisting of chokes 120, 121, 122 andcapacitors I23 and 124 is charged for the duration of the pulse acrossresistor 101, and after the pulse disappears, the circuit oscillates asshown in FIG. 10. Therefore, the tube 110 is driven by the oscillatingcurrent shown in FIG. 10, and the tube is driven in a high-frequencymode in accordance with the invention.

It is to be noted that the circuit of FIG. 13 uses a particularmodulator which responds only to positive pulses at terminals 86 and 87.Clearly, the circuit could be modified so that both positive andnegative pulses could drive the modulator. Moreover, it will be apparentthat all biasing voltages could be directly derived from thehigh-frequency circuit by means of relatively small transformers.

It will also be understood that the lamp 110 could have been replaced bya general load which requires a generally sinusoidal wave shape. By wayof example, a winding could be taken from one of chokes 120, I21 and 122to serve as a highfrequency input to a biasing voltage circuit.

Referring next to FIG. 14, there is illustrated a circuit using thegeneral concepts of the circuit of FIG. 9 where, however, a plurality ofgas discharge lamps are operated from the common modulator 62. Thus, inFIG. 14 there is shown three lamps 200, 201 and 202 which may be anydesired type of gas discharge lamp, such as fluorescent tube, and eachof the tubes 200 to 202 is provided with-a respective oscillator network203, 204 and 205. The oscillator networks 103, I04 and are each of thecurrent-fed variety as in the case of FIG. 9, and it will be seen thatthey are each identical to the networks of FIG. 9 if the coil 71 of FIG.9 is removed. More specifically, it has been found in connection withcircuits of the type shown in FIG. 9 that coil 71 can be eliminated.Preferably, however, coil 71 may have an extremely low inductance, forexample, I microhenry, as compared to a typical value of millihenrysfor. coil 72, where the small inductive impedance of coil 71preventshigh surge currents from being drawn from modulator 62 directlythrough capacitor 73 which could damage modulator 62. A small resistancecould also perform this current-limiting effect.

In FIG. 14 the pulse-forming networks 203 to 205 consist of chokes 206,207 and 208, respectively, and capacitors 209, 210 and 211,respectively. Each of the individual circuits are then connected inseries with suitable isolating impedances 212, 213 and 214 whichessentially decouple the parallel-connected circuits from one anotherand provides the currentlimiting impedance necessary to limit themagnitude of the pulse current drawn from modulator 62 directly throughcapacitors 209, 210 or 211. Impedances 212, 213 and 214 may becapacitors.

When using a circuit of the type shown in FIG. 14, it will be apparentthat substantial economies are obtained since only a single pulsemodulator 62 is needed for a plurality of individual lamps. Note thatany number of lamps can be used. Moreover, the size of the componentsused in oscillating networks 203, 204 and 205 is kept small since theyeach operate only in connection with a single lamp. This also makes itpossible to locate the oscillating networks close to the lamps so thatlong transmission lines are not needed to convey the highfrequency powerfrom the oscillating network to its particular gas discharge lamp.

FIG. 15 is similar to FIG. 14, but shows a modified version of theoscillating network of FIG. 8 used in connection with the lamps 200, 201and 202. Thus, in FIG. 15 the oscillating networks consist of theseries-connected chokes 220, 221 and 122, respectively, and capacitors223, 224 and 225, respectively, for the tubes 200, 201 and 202. Each ofthe oscillating networks of FIG. 15 is essentially identical to thenetwork of FIG. 8 with the choke 65 and capacitor 67 removed. Tests havedemonstrated that these components may be eliminated to develop thesimpler series oscillating circuit shown in FIG. 15.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited,not by the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. A gas discharge lamp energizing circuit comprising, in combination: avoltage source, a pulse modulator means and a gas discharge lamp; saidgas discharge lamp having a pair of terminals; said voltage source,pulse modulator means and gas discharge lamp pair of terminals directlyconnected in series by circuit connection means; said circuit connectionmeans being free of oscillation circuit means; said pulse modulatormeans being alternately conductive and nonconductive; and an oscillatingnetwork connected in parallel with said gas discharge lamp; saidoscillating network including at least a first choke and at least afirst capacitor connected in parallel with one another.

2. The circuit of claim 1 wherein the period of said oscillating networkis substantially independent of the period of said pulse modulatormeans.

3. The energizing circuit of claim 1 wherein said oscillating networkhas characteristic impedance substantially less than the impedance ofsaid lamp when said lamp is in conduction.

4. The energizing circuit of claim 1 wherein said oscillating networkfurther includes a second choke and a second capacitor; said secondchoke connected in series with said first choke and said secondcapacitor.

5. The energizing circuit of claim 1 wherein said oscillating networkfurther includes a second choke connected in series with both said firstchoke and said first capacitor.

6. A relatively high frequency AC voltage generator for driving alighting load from a source of input voltage which has a frequency inthe range of from zero cycles per second to a relatively low frequencyas compared to said relatively high frequency of said AC voltagegenerator; said AC voltage generator comprising, in combination: saidsource of input voltage, a pulse modulator means which is sequentiallyswitched between conduction and nonconduction at a given frequency, agas discharge type lighting load, and a single oscillating network; saidsingle oscillating network being connected in parallel with saidlighting load, said source of input voltage, said pulse modulator meansand said single oscillating network being directly connected in a closedseries circuit; said single oscillating network being tuned to a singlefixed frequency.

7. The AC voltage generator of claim 6 wherein said oscillating networkhas a charadtei'istic impedance substantially less than the impedance ofsaid gas discharge load when said gas discharge load is in conduction.

8. The AC voltage generator of claim 6 wherein said oscillating networkfurther includes a second choke and a second capacitor; said secondchoke connected in series with said first choke and said secondcapacitor.

9. The AC voltage generator of claim 6 wherein said oscillating networkfurther includes a second choke connected in series with both said firstchoke and said first capacitor.

10. The circuit of claim 6 wherein said oscillating network has acharacteristic impedance approximately equal to the impedance of saidgas discharge load when said load is in conduction.

11. A gas discharge lamp energizing circuit comprising, in combination,a voltage source, a single pulse modulator means, a plurality ofoscillating networks, and a plurality of gas discharge lamps; each ofsaid oscillating networks being connected in circuit relation with arespective one of said gas discharge lamps; said voltage source, pulsemodulator means and said circuit of said respective oscillating networksand gas discharge lamps; said voltage source, pulse modulator means andsaid circuit of said respective oscillating networks and gas dischargelamps being connected in series; said pulse modulator means beingaltematel conductive and nonconductive thereby to apply voltage pu sesto said oscillating network, and

thereby to energize said gas discharge lamps.

12. The circuit of claim 1 1 wherein said oscillating networks eachinclude a series-connected capacitor and inductor connected in parallelwith their said respective gas discharge lamps.

13. The circuit of claim 11 wherein said oscillating networks eachinclude a parallel-connected capacitor and inductor connected inparallel with their said respective gas discharge lamps.

14. A gas discharge lamp energizing circuit comprising, in combination:a voltage source, a single pulse modulator means, a plurality ofoscillating network means, a plurality of gas discharge lamps eachconnected in parallel with a respective one of said plurality ofoscillating network means, and a plurality of coupling impedance meansrespectively connected in series with each of said gas discharge lamps;said plurality of series-connected gas discharge lamps and respectivecoupling impedance means connected in series with said single pulsemodulator means.

15. The circuit of claim 14 wherein each of said plurality of couplingimpedance means consists of a capacitor.

* II! i I

1. A gas discharge lamp energizing circuit comprising, in combination: avoltage source, a pulse modulator means and a gas discharge lamp; saidgas discharge lamp having a pair of terminals; said voltage source,pulse modulator means and gas discharge lamp pair of terminals directlyconnected in series by circuit connection means; said circuit connectionmeans being free of oscillation circuit means; said pulse modulatormeans being alternately conductive and nonconductive; and an oscillatingnetwork connected in parallel with said gas discharge lamp; saidoscillating network including at least a first choke and at least afirst capacitor connected in parallel with one another.
 2. The circuitof claim 1 wherein the period of said oscillating network issubstantially independent of the period of said pulse modulator means.3. The energizing circuit of claim 1 wherein said oscillating networkhas characteristic impedance substantially less than the impedance ofsaid lamp when said lamp is in conduction.
 4. The energizing circuit ofclaim 1 wherein said oscillating network further includes a second chokeand a second capacitor; said second choke connected in series with saidfirst choke and said second capacitor.
 5. The energizing circuit ofclaim 1 wherein said oscillating network further includes a second chokeconnected in series with both said first choke and said first capacitor.6. A relatively high frequency AC voltage generator for driving alighting load from a source of input voltage which has a frequency inthe range of from zero cycles per second to a relatively low frequencyas compared to said relatively high frequency of said AC voltagegenerator; said AC voltage generator comprising, in combination: saidsource of input voltage, a pulse modulator means which is sequentiallyswitched between conduction and nonconduction at a given frequency, agas discharge type lighting load, and a single oscillating network; saidsingle oscillating network being connected in parallel with saidlighting load, said source of input voltage, said pulse modulator meansand said single oscillating network being directly connected in a closedseries circuit; said single oscillating network being tuned to a singlefixed frequency.
 7. The AC voltage generator of claim 6 wherein saidoscillating network has a characteristic impedance substantially lessthan the impedance of said gas discharge load when said gas dischargeload is in conduction.
 8. The AC voltage generator of claim 6 whereinsaid oscillating network further includes a second choke and a secondcapacitor; said second choke connected in series with said first chokeand said second capacitor.
 9. The AC voltage generator of claim 6wherein said oscillating network further includes a second chokeconnected in series with both said first choke and said first capacitor.10. The circuit of claim 6 wherein said oscillating network has acharacteristic impedance approximately equal to the impedance of saidgas discharge load when said load is in conduction.
 11. A gas dischargelamp energizing circuit comprising, in combination, a voltage source, asingle pulse modulator means, a plurality of oscillating networks, and aplurality of gas discharge lamps; each of said oscillating networksbeing connected in circuit relation with a respective one of said gasdischarge lamps; said voltage source, pulse modulator means and saidcircuit of said respective oscillating networks and gas discharge lampsbeing connected in series; said pulse modulator means being alternatelyconductive and nonconductive, thereby to apply voltage pulses to saidoscillating networks, and thereby to energize said gas discharge lamps.12. The circuit of claim 11 wherein said oscillating networks eachinclude a series-connected capacitor and inductor connected in parallelwith their said respective gas discharge lamps.
 13. The circuit of claim11 wherein said oscillating networks each include a parallel-connectedcapacitor and inductor connected in parallel with their said respectivegas discharge lamps.
 14. A gas discharge lamp energizing circuitcomprising, in combination: a voltage source, a single pulse modulatormeans, a plurality of oscillating network means, a plurality of gasdischarge lamps each connected in parallel with a respective one of saidplurality of oscillating network means, and a plurality of couplingimpedance means respectively connected in series with each of said gasdischarge lamps; said plurality of series-connected gas discharge lampsand respective coupling impedance means connected in series with saidsingle pulse modulator means.
 15. The circuit of claim 14 wherein eachof said plurality of coupling impedance means consists of a capacitor.